Absorption refrigeration systems are well known to the art. The basic principle of these systems is identical to that of the single-stage compression system except for the manner in which the pressure of the refrigerant vapor is increased to the level required for condensation. In an absorption system, the compressor of a compression system is replaced by an "absorber" and a "generator." Then, instead of compressing a low-pressure refrigerant vapor, the refrigerant vapor is first absorbed by a weak solution of refrigerant and is then pumped into a generator where it is heated back to the vapor phase.
Further describing an absorption system, a generator heats an absorbent solution, preferably ammonia and water, so as to release the refrigerant (ammonia) in vapor form, from solution in the generator as previously described. The refrigerant vapor then passes through an analyzer to a rectifier and then to a condenser where it is condensed at a relatively high pressure by the ambient air or by fluids such as water or water/glycol mixtures. The condensed ammonia passes through a pressure reduction device and a refrigerant heat exchanger to an evaporator where the pressure is further reduced and the refrigerating effect is accomplished. The low pressure vapor then flows back through the refrigerant heat exchanger to a solution absorber heat exchanger where it comes into contact with a weak solution of refrigerant fluid flowing from the generator. In the absorber heat exchanger, the weak solution absorbs a portion of the low pressure vapor with the resulting solution passing into an absorber cooled by ambient air or by fluids such as water or water/glycol mixtures. This results in the remaining ammonia vapor being absorbed in the absorbent solution. The strong solution thus formed passes through a solution pump, to help overcome the difference between the low pressure and the high pressure sides of the system, to the rectifier, the absorber heat exchanger, and the generator, where the cycle repeats itself. The present invention addresses a new design hydraulic pump whose function is to pump the absorbent solution from the low pressure side to the high pressure side of the system.
As further background, some prior art systems have used diaphragm pumps to transfer the absorbent solution from the low pressure side to the high pressure side of the system. These prior art diaphragm pumps are driven by a hydraulic fluid that is pulsed against a diaphragm to push absorbent solution to the high side. When the hydraulic fluid pressure is released, the pressure from the low side of the system pushes new absorbent solution against the diaphragm, causing it to return to its original position.
Unfortunately, the operating capabilities of prior art hydraulic pumps are limited by the fact that when the entering pump pressure is below approximately 10 psig (25 psia), the pump bypasses most of the oil normally used for pulsing the diaphragm within the pump mechanism itself through a relief valve. This causes the pump to operate inefficiently, and may even cause the pump to seize up and stop.
More particularly, as the absorber pressure decreases, the movement of the diaphragm from its upper position (pushing refrigerant solution into the high pressure side of the system) to its lower position ("pulling" refrigerant solution from the low pressure side of the system) is also decreased. Therefore, the pump merely moves oil in its own enclosure. The oil gets very hot and can cause the pump to malfunction. From the unit's operating parameters, the 25 psia at the pump equates to approximately a 5.degree. F. at the evaporator at its lowest temperature.
A need therefore exists for a solution pump that can pump absorbent solution from the low side to the high side of an absorption refrigeration system even when the pressure on the low side is extremely low. The present invention addresses that need.